1. Field of Invention
This invention pertains to a system for delivering a stent to a site in a body lumen. More particularly, this invention pertains to a stent delivery system with improved structure between sliding tubular members.
2. Description of the Prior Art
Stents are widely used for supporting a lumen structure in a patient""s body. For example, stents may be used to maintain patency of a coronary artery, other blood vessel or other body lumen.
Commonly, stents are commonly metal, tubular structures. Stents are passed through the body lumen in a collapsed state. At the point of an obstruction or other deployment site in the body lumen, the stent is expanded to an expanded diameter to support the lumen at the deployment site.
In certain designs, stents are open-celled tubes which are expanded by inflatable balloons at the deployment site. Other stents are so-called xe2x80x9cself-expandingxe2x80x9d stents. Self-expanding stents do not use balloons or other application of force to a collapsed stent to cause the expansion of the stent. An example of a self-expanding stent is a coil structure which is secured to a stent delivery device under tension in a collapsed state. At the deployment site, the coil is released so that the coil can expand to its enlarged diameter. Other self-expanding stents are made of so-called shape-memory metals such as nitinol. Such shape-memory stents experience a phase change at the elevated temperature of the human body. The phase change results in expansion from a collapsed state to an enlarged state.
A delivery technique for shape-memory alloy stents is to mount the collapsed stent on a distal end of a stent delivery system. Such a system would include an outer tubular member and an inner tubular member. The inner and outer tubular members are axially slideable relative to one another. The stent (in the collapsed state) is mounted surrounding the inner tubular member at its distal end. The outer tubular member (also called the outer sheath) surrounds the stent at the distal end.
Prior to advancing the stent delivery system through the body lumen, a guide wire is first passed through the body lumen to the deployment site. The inner tube of the delivery system is hollow throughout its length such that it can be advanced over the guide wire to the deployment site.
The combined structure (i.e., stent mounted on stent delivery system) is passed through the patient""s lumen until the distal end of the delivery system arrives at the deployment site within the body lumen. The deployment system may include radio-opaque markers to permit a physician to visualize positioning of the stent prior under fluoroscopy to deployment.
At the deployment site, the outer sheath is retracted to expose the stent. The exposed stent is now free to expand within the body lumen. Following expansion of the stent, the inner tube is free to pass through the stent such that the delivery system can be removed through the body lumen leaving the stent in place at the deployment site.
Throughout the procedure, it may be desirable to inject a contrast media (a liquid which can be visualized under fluoroscopy). The contrast media is injected into the space defined between opposing surfaces of the inner and outer tubes. The outer tube has side ports extending through the sidewall of the outer tube near its distal end. The contrast media is injected into the body lumen through the side ports.
Prior art stent delivery systems use inner and outer tubes of generally uniform diameters and circular cross-section throughout their length. This design relies upon the dynamics of fluid flow to retain spacing between the tubes.
In the event the outer diameter of the inner prior art tube is substantially less than the inner diameter of the outer prior art tube, the inner tube could bend relative to the outer tube such that surfaces of the inner tube abut surfaces of the outer tube. As a result, axial forces applied to advance the stent delivery system could be stored in the bent inner tube. Such energy could be suddenly released with sudden and undesired rapid advance or retraction of the distal tip of the tubes when the inner tube straighten. Also, contact between the surfaces of the inner and outer tubes members can result in friction between the members resisting relative moment between the tubes.
The likelihood of the sudden jumping phenomena could be reduced by having the inner and outer tube diameters be as close as possible. However, such close tolerances result in a very small annular gap between the inner and outer tubes which results in increased resistance to flow of contrast media between the inner and outer tube.
Another flaw with prior devices is the absence of comfortable grips to permit the user (such as an interventional cardiologist or a radiologist) to comfortably manipulate the inner tube relative to the outer tube and to readily visualize the relative positioning between the inner tube and outer tubes in their axial alignment.
It is an object of the present invention to provide improved structures for a stent delivery system.
According to a preferred embodiment of the present invention, a stent delivery system is disclosed for delivering a stent to a deployment site in a body lumen of a patient. The stent delivery system includes outer and inner elongated, flexible tubular members each having a distal and proximal ends. The outer tubular member is sized to be passed through the body lumen with the distal end advanced to the deployment site and with the proximal end remaining external of the patient""s body for manipulation by an operator. The inner tubular member is sized to be received within the outer tubular member. The outer tubular and inner tubular members are axially slideable relative to one another between a transport position and the deploy position. The inner tubular member has a stent attachment location at its distal end. The stent attachment location is covered by the outer tubular member when the inner and outer tubular members are in the transport position. The stent attachment location is exposed when the inner and outer tubular members are in the deploy position. A spacer member is disposed between the inner and outer tubular members. The spacer member maintains spacing between the inner and outer tubular members. Opposing surfaces of the inner and outer tubular members define a first lumen extending from the proximal end towards the distal end of the outer tubular member. An admission port is provided in communication with the first lumen at the proximal end of the outer tubular member. A discharge port is formed through the outer tubular member in communication with the first lumen at the distal end of the outer tubular member.